Ti/Pd Bimetallic Systems for the Efficient Allylation of Carbonyl Compounds and Homocoupling Reactions
作者:Alba Millán、Araceli G. Campaña、Btissam Bazdi、Delia Miguel、Luis Álvarez de Cienfuegos、Antonio M. Echavarren、Juan M. Cuerva
DOI:10.1002/chem.201003315
日期:2011.3.28
The allylation, crotylation and prenylation of aldehydes and ketones with stable and easily handled allylic carbonates is promoted by a Ti/Pd catalytic system. This Ti/Pd bimetallic system is especially convenient for the allylation of ketones, which are infrequent substrates in other related protocols, and can be carried out intramolecularly to yield five‐ and six‐membered cyclic products with good
Ti / Pd催化体系可促进醛和酮与稳定且易于处理的烯丙基碳酸酯的烯丙基化,丁酰化和烯丙基化。这种Ti / Pd双金属体系特别适合于酮的烯丙基化,酮是其他相关规程中不常见的底物,并且可以在分子内进行生产,从而产生具有良好立体选择性的五元和六元环状产物。此外,Ti / Pd介导的还原反应和Würtz型二聚反应可以很容易地从碳酸烯丙酯和羧酸酯中进行。
Activation of manganese metal by a catalytic amount of PbCl2 and Me3SiCl
Allylation of carbonyl compounds and the Reformatsky-type reaction are performed with manganesemetal which is activated by addition of a catalyticamount of Me3SiCl and PbCl2 in THF.
A lead-promoted allylation of carbonylcompounds with allyl bromide in a Pb/Bu4NBr/Me3SiCl/DMF system has been performed in good yields with high chemoselectivities: RCHO > R1R2CO > R1CH(OH)CO2R2>> R1CO2R2, lactone, (RCO)2O, and RCOCl.
Synthesis of Tetrahydrofurans by Cyclization of Homoallylic Alcohols with Iodine/Iodine(III)
作者:Ramon S. Vasconcelos、Luiz F. Silva、Athanassios Giannis
DOI:10.1021/jo102413u
日期:2011.3.4
Tetrahydrofuran derivatives can be obtained by cyclofunctionalization of homoallylicalcohols bearing a terminal double bound by using [hydroxy(tosyloxy)iodo]benzene (HTIB, Koser’s reagent) in the presence of a catalytic amount of I2 (20 mol %) in MeOH under mild conditions. This transformation is an overall5-endo-trig cyclization, which occurs by two different pathways. The first is a 4-exo-trig
to produce unisolable allylchromium species which add efficiently to aldehydes or ketones with high degree of stereo- and chemoselectivity. Particularly, high threo selectivity is observed in the reaction of aldehydes and 1-bromo-2-butene and is ascribed to a chair-like six-membered transition state. Simple reduction of allylic and benzylic halides produces biallyls and bibenzyls, while gem-dibromocyclopropanes